Fix TypeScript types with Node16/NodeNext module resolution

[Gerrit0]

Summary

TypeScript with the Node16 or NodeNext setting for "module" in tsconfig.json will read the package exports map. This adds types entries to package.json so that it can be used in those settings. The types key is left in place so that the package types still work for users with "module": "CommonJS".

TypeScript requires different declaration files (even though the same content works for both) so that it can distinguish between import/require. For clarity, the build script now writes to require.d.ts (not .d.cts for compatibility with old TS versions) and import.d.mjs

Test results and supporting details

Tested by adding the build directory as a dependency, and checking:

Config	main	main types	forLegacyNode	forLegacyNode types
.mts file with NodeNext	✅	✅	✅	✅
.cjs file with NodeNext	✅	✅	✅ (require is error, can be dynamically imported)	✅ (types can be imported)
.ts file with CommonJS using import bcd from transpiled into require	✅	✅	❌ (no support for exports, would have to rename files, anyone who runs into this should probably be using Node16/NodeNext anyways)	❌
.ts file with CommonJS using import x = require("@mdn/browser-compat-data")	❌ (ts thinks the value is under .default, not many TS users even know this is a feature, don't think this matters)	❌	❌	❌

Related issues

Fixes #17964

[queengooborg]

Alright, let's get this landed, thank you for your PR! Welcome to BCD!